Method and apparatus for phase and/or copy window control for use with a domain expansion recording medium and record carrier

ABSTRACT

The present invention relates to a method, apparatus and record carrier for controlling read-out and/or synchronization between an external magnetic field and written data during a reading operation from a magneto-optical recording medium comprising a storage layer and a read-out layer. An expanded domain leading to a pulse in a reading signal is generated in said read-out layer by copying a mark region from said storage layer to said read-out layer upon heating by a radiation power and with the help of the external magnetic field. The waveform of the reading signal is analyzed, and the analyzing result is used for correcting a phase deviation and/or for controlling a copy window size of the mark copying. Thereby, phase errors can be corrected for any size of the copy window. Even small changes in the copy window can be detected and corrected.

The present invention relates to a method, apparatus and record carrierfor controlling read-out from a magneto-optical recording medium and/orfor controlling the phase between an external magnetic field and datawritten to the magneto-optical recording medium, such as a MAMMOS(Magnetic AMplifying Magneto-Optical System) disk, comprising arecording or storage layer and an expansion or read-out layer.

In magneto-optical storage systems, the minimum width of the recordedmarks is determined by the diffraction limit, i.e. by the NumericalAperture (NA) of the focussing lens and the laser wavelength. Areduction of the width is generally based on shorter wavelength lasersand higher NA focussing optics. During magneto-optical recording, theminimum bit length can be reduced to below the optical diffraction limitby using Laser Pulsed Magnetic Field Modulation (LP-MFM). In LP-MFM, thebit transitions are determined by the switching of the field and thetemperature gradient induced by the switching of the laser. For read-outof the small crescent-shaped marks recorded in this way, Magnetic SuperResolution (MSR) or Domain Expansion (DomEx) methods have been proposed.These technologies are based on recording media with severalmagneto-static or exchange-coupled RE-TM layers. According to MSR, aread-out layer on a magneto-optical disk is arranged to mask adjacentbits during reading, while, according to domain expansion, a domain inthe center of a spot is expanded. The advantage of the domain expansiontechnique over MSR results in that bits with a length below thediffraction limit can be detected with a similar signal-to-noise ratio(SNR) as bits with a size comparable to the diffraction limited spot.MAMMOS is a domain expansion method based on magneto-statically coupledstorage and read-out layers, wherein a magnetic field modulation is usedfor expansion and collapse of expanded domains in the read-out layer.

In the above-mentioned domain expansion techniques, like MAMMOS, awritten mark from the storage layer is copied to the read-out layer uponlaser heating with the aid of an external magnetic field. Due to the lowcoercivity of this read-out layer, the copied mark will expand to fillthe optical spot and can be detected with a saturated signal level whichis independent of the mark size. Reversal of the external magnetic fieldcollapses the expanded domain. A space in the storage layer, on theother hand, will not be copied and no expansion occurs. Therefore, nosignal will be detected in this case.

During MAMMOS read-out, synchronization between the data and theexternal magnetic field (and the laser power in case of a pulsedstrategy) is required. The reason for this requirement is that a smallphase error already introduces a false peak when the copy window isclose to its maximum size for correct read-out. For this purpose timingfields and/or a wobble in the track can be used. In this way, quitereasonable frequency control is possible, but phase errors are verydifficult to avoid. However, for MAMMOS no phase control method has beenproposed yet.

Furthermore, the laser power used in the read-out process should be highenough to enable copying. On the other hand, a higher laser power alsoincreases the overlap of the temperature-induced coercivity profile andthe stray field profile of the bit pattern. The coercivity H_(c)decreases and the stray field increases with increasing temperature.When this overlap becomes too large, correct read-out of a space is nolonger possible due to false signals generated by neighboring marks. Thedifference between this maximum and the minimum laser power determinesthe power margin, which decreases strongly with decreasing bit length.Experiments have shown that with the current methods, bit lengths of0.10 μm can be correctly detected, but at a power margin of virtuallynothing (1 bit of a 16 bit DAC). Therefore, a method has been proposedto use the occurrence and number of false read-out signals to measurethe copy window. This measurement can be used to correct the read dataand to correct the size of the copy window (e.g. by changing the laserpower). However, according to this known method, a correction of thecopy window size is only possible when the window size changessufficiently to generate false peaks, so that an averaging method isrequired to refine the control.

It is an object of the present invention to provide a method, apparatusand record carrier for providing a copy window and/or phase control fora domain expansion read-out process.

This object is achieved by a method as claimed in claims 1 or 6, by anapparatus as claimed in claims 21 or 22, and by a record carrier asclaimed in claim 26.

Accordingly, any deviation in the window size or the phase, which has aninfluence on the waveform of the reading signal, can be readily detectedby analyzing the waveform of the reading signal. Thereby, a fine-tuningfeature can be provided, where an error correction is already possiblebefore at least partially uncorrectable errors occur in the readingsignal. Moreover, much less averaging is required, so that even verysmall non-uniformities or brief fluctuations in the magnetic field orlaser power can be dealt with.

The correction step for correcting the phase deviation or error may beperformed by shifting the timing of the external magnetic field.Furthermore, the phase correction step may be based on predeterminedcorrection rules which depend on a write strategy and/or a read strategyused. Thus, quite simple rules can be defined for many combinations ofwrite and read strategies. In particular, the correction rules maydefine a correction amount and direction. A correction rule which maydefine e.g. an amount and a direction of the phase correction can thenbe derived directly from a detected amount of change in the waveform ofthe reading signal.

According to an advantageous further development, correction rules maybe defined for an additional copy window correction. Such a combinationof the phase control with an additional or simultaneous copy windowcontrol yields an even better control. The copy window size controllingstep may be performed by controlling the radiation power and/or thestrength of the external magnetic field.

According to another advantageous further development, synchronizationphase errors detected between the external magnetic field and thewritten data may be used in the analyzing step. When phase errors in thesynchronization and the size of the copy window are both included in theanalysis, phase errors up to 180° can be detected and corrected for anysize value of the copy window.

The analyzing step may be applied either to a reading signal obtained byreading a test area provided on the recording medium or to a readingsignal obtained by reading written user data.

Preferably, the analyzing step may comprise comparing the timing of therising edge and/or the duration of a predetermined pulse of the readingsignal with a reference value. Thus, any deviation in thesynchronization phase or copy window size can be detected simply on thebasis of changes in the reading pulses. The predetermined pulse may bethe first pulse of a code run-length. The duration may be determined bydetecting the pulse amplitude of the predetermined pulse after a filteroperation.

According to another advantageous further development, the analyzingstep may be performed by using information from a look-up table. Thelook-up table may be updated on the basis of information read from therecording medium. The information may define a relation between saidwaveform and at least one of a phase error and a copy window size. Thelook-up table may be provided by a control program of a driver functionused for generating said external magnetic field.

Strategy information defining a write strategy of the recording mediummay be written on the recording medium, to be used in said analyzingstep. In particular, the strategy information may be used for generatinga reference waveform used in the analyzing step.

As regards the reading apparatus, the analyzing means may comprisestoring means for storing information defining a relation between thewaveform and at least one of a phase error and a copy window size.Furthermore, the analyzing means may comprise comparing means forcomparing the analyzed waveform on the basis of the relation stored inthe storing means.

Other advantageous further developments are defined in the dependentclaims.

The present invention will be described hereinafter on the basis of apreferred embodiment and with reference to the accompanying drawings, inwhich:

FIG. 1 shows a diagram of a magneto-optical disk player according to thepreferred embodiment,

FIG. 2A shows waveforms of a generated overlap as a function of the sizeof the copy window,

FIG. 2B shows waveforms of an external magnetic field as a function ofthe synchronization phase,

FIGS. 3A to 3E show waveforms of a reading signal as a function of thesynchronization phase for different copy window sizes,

FIG. 4 shows a look-up table indicating pulse changes in the readingsignal for different phase values and copy window sizes in case of afirst write strategy, and

FIG. 5 shows a look-up table indicating pulse changes in the readingsignal for different phase values and copy window sizes in case of asecond write strategy.

A preferred embodiment will now be described on the basis of a MAMMOSdisk player as indicated in FIG. 1.

FIG. 1 schematically shows the construction of the disk player accordingto preferred embodiments. The disk player comprises an optical pick-upunit 30 having a laser light radiating section for irradiation of amagneto-optical recording medium or record carrier 10, such as amagneto-optical disk, with light that has been converted, duringrecording, to pulses with a period synchronized with code data, and amagnetic field applying section comprising a magnetic head 12 whichapplies a magnetic field in a controlled manner at the time of recordingand playback on the magneto-optical disk 10. In the optical pick-up unit30 a laser is connected to a laser driving circuit which receivesrecording and read-out pulses from a recording/read-out pulse adjustingunit 32 to thereby control the pulse amplitude and timing of the laserof the optical pick-up unit 30 during a recording and read-outoperation. The recording/read-out pulse adjusting circuit 32 receives aclock signal from a clock generator 26 which may comprise a PLL (PhaseLocked Loop) circuit.

It is to be noted that, for reasons of simplicity, the magnetic head 12and the optical pick-up unit 30 are shown on opposite sides of the disk10 in FIG. 1. However, according to the preferred embodiment, theyshould be arranged on the same side of the disk 10.

The magnetic head 12 is connected to a head driver unit 14 and receives,at the time of recording, code-converted data via a phase adjustingcircuit 18 from a modulator 24. The modulator 24 converts inputrecording data to a prescribed code.

At the time of playback, the head driver 14 receives a clock signal, viaa playback adjusting circuit 20, from the clock generator 26, theplayback adjusting circuit 20 generating a synchronization signal foradjusting the timing and amplitude of pulses applied to the magnetichead 12. A recording/playback switch 16 is provided for switching orselecting the respective signal to be applied to the head driver 14 atthe time of recording and at the time of playback.

Furthermore, the optical pick-up unit 30 comprises a detector fordetecting laser light reflected from the disk 10 and for generating acorresponding reading signal applied to a decoder 28 which is arrangedto decode the reading signal to generate output data. Furthermore, thereading signal generated by the optical pick-up unit 30 is applied to aclock generator 26 in which a clock signal obtained from embossed clockmarks of the disk 10 is extracted, and which applies the clock signalfor synchronization purposes to the recording pulse adjusting circuit32, the playback adjusting circuit 20, and the modulator 24. Inparticular, a data channel clock may be generated in the PLL circuit ofthe clock generator 26.

In the case of data recording, the laser of the optical pick-up unit 30is modulated with a fixed frequency corresponding to the period of thedata channel clock, and the data recording area or spot of the rotatingdisk 10 is locally heated at equal distances. Additionally, the datachannel clock output by the clock generator 26 controls the modulator 24to generate a data signal with the standard clock period. The recordingdata are modulated and code-converted by the modulator 24 to obtainbinary run-length information corresponding to the information of therecording data.

The structure of the magneto-optical recording medium 10 may correspondto the structure described in the JP-A-2000-260079.

The occurrence of false signals due to a large overlap (e.g. laser powertoo high) should normally be avoided. If the correct data in the storagelayer is known, the occurrence and number of false peaks gives directinformation on the spatial width of the copy window which is directlyrelated to the thermal laser profile. However, this control can befurther improved if a change in the waveform of the reading signal (i.e.MAMMOS peaks) is additionally considered and analyzed. The waveforminformation obtained provides a direct way to correct or control thecopy window size (e.g. laser power and/or field amplitude) and/or phasedeviations in the synchronization between the external magnetic fieldand the written data.

In the preferred embodiment shown in FIG. 1, a control unit 25 isprovided for applying control signals Cp and Cw to the head driver 14 orthe playback adjusting circuit 20 and/or to the optical pick-up unit 30,respectively. The control signal Cp applied to the head driver 14 or,alternatively, to the playback adjusting circuit 20, can be used toadjust the timing of the pulses applied to the magnetic head, so as toadjust the timing or phase of the external magnetic field. The othercontrol signal Cw applied to the optical pick-up unit 30 can be used foradjusting the driving current of a laser diode or another radiationsource, so as to adjust the optical radiation or laser power used forheating the disk 10, and hence the size of the copy window. The twocontrol signals Cp and Cw may be provided as alternative or combinedcontrol signals. Furthermore, a sole or combined field amplitude controlcan alternatively be used for copy window control.

The control unit 25 receives a comparison result from a comparing unit22 which compares the result of an analysis of the waveform (e.g. shapeof MAMMOS peaks) of the read-out signal obtained from the decoder 28with reference data or a reference waveform stored in a non-volatilememory, e.g. a look-up table 23. The analysis is performed by ananalyzing unit 21 which receives the read-out signal from the decoder 28and is arranged to determine a change, for example, in the first pulseor peak of a run-length of the read-out signal.

When both phase errors in the synchronization and the size of the copywindow are included in the analysis of the read-out waveform by theanalyzing unit 21, phase errors as large as +/−180° can be detected andcorrected for any value of the copy window. It is noted that bothwritten user data as well as dedicated test areas can be used for thispurpose.

Characteristic changes in the waveform of the reading signal and theirrelation to the copy window size and the phase error in thesynchronization between the external magnetic field and the written datawill be explained hereinafter with reference to signaling diagrams shownin FIGS. 2A to 3E. It is to be noted that in each of these diagrams thehorizontal axis is a time axis.

FIG. 2A shows overlap signals indicating the overlap between the copywindow and a bit pattern for the case of a 50% duty cycle write strategy(i.e. mark length corresponds to 50% of the channel bit length b) fordifferent copy window sizes (i.e. w=0 to 2b). It is to be noted that thecopy window size w=0 basically corresponds to the bit pattern on thedisk 10.

FIG. 2B shows signals indicating the modulated external field fordifferent values of the synchronization phase, ranging from 0° to 360.

The solid lines in FIGS. 3A to 3E denote signaling diagrams indicatingMAMMOS or reading signals obtained from the decoder 28 and correspondingto each combination of the window sizes w (up to a window size equal tothe channel bit length b (for example w=b)) and phases, while theexternal field is indicated as a reference signal by the dashed lines(the dashed lines refer to the magnetic field waveforms of FIG. 2B). Ascan be gathered from these signaling diagrams, characteristic changes inthe waveform of the reading signals can be observed. These changes canbe analyzed to derive a required correction or control value for thecopy window size and/or the synchronization phase of the externalmagnetic field. In particular, a change in the pulse width of the firstpulse of a run-length in the reading signal can be used as a criterionfor the phase and/or window control function. Run-lengths with more thanone MAMMOS peak occur in cases of larger copy window sizes, as indicatedin the FIGS. 3C to 3E. The change in the pulse width may be detected bymonitoring or analyzing at least one of, for example, the timing of theleading or rising edge of the first run-length pulse. Alternatively, theduration of the first pulse of a run-length may be monitored oranalyzed. The duration may be derived from a detection of the pulseamplitude at the output of a filter circuit which may be any circuithaving a low-pass filter characteristic, for example, the detection orreading system of the optical pick-up unit 30.

Hereinafter, the changes will be categorized as follows (using a“saturated” pulse or signal s without any change in the pulse width as areference value):

“b=s” indicates no change in the waveform (as for example in the 0 or315° signal of FIG. 3B);“b<s” indicates a small change in the waveform (as for example in the270° signal of FIG. 3B);“b<<s” indicates a medium change in the waveform (as for example in the225° signal of FIG. 3B); and“b<<<s” indicates a large change in the waveform (as for example in the180° signal of FIG. 3B).

The signals of FIGS. 3A to 3E are summarized in the table shown in FIG.4. Each column corresponds to a different copy window size w, whereaseach row corresponds to a different phase of the external magneticfield. It is clear that any deviation or change in copy window size w orphase outside the areas “b=s” (indicated by bold lines) may readily bedetected by comparing e.g. the timing of the rising edges of the firstMAMMOS peak of each run-length with that of the external magnetic field,and/or by comparing the length of the first peak of each run-length withthe saturated reference signal (i.e. external magnetic field). Also,violations of run-length constraints due to false peaks could beincluded.

In particular, pulse widths shorter than the saturated signal can bedetected directly with a very high bandwidth detection system or bymeasuring the amplitude of the signals. In the latter case, a shorterpulse will give in general a smaller signal due to limitation by thebandwidth of the detection system and/or a separate low-pass filter. Inthis case, the length of the peak is directly related to the signalamplitude and can thus be derived from the amplitude.

Specific run-lengths in the written data can be denoted as follows. Theexpression “−In” denotes a space run-length with a durationcorresponding to n channel bits (minimum space or mark regions), whilethe expression “In” denotes a mark run-length with a durationcorresponding to n channel bits. For correct read-out, in the case of a100% write strategy, the copy window should be smaller than half thechannel bit length b. In this case, each mark channel will yield oneMAMMOS peak and no peaks will be generated for space channels. Thus,detection of m subsequent peaks indicates an Im mark run-length, whereass missing peaks indicate a −Is space run-length. For larger windowsizes, for example 0.5b<w<2.5b, MAMMOS peaks will also be generated forspace regions near a mark region because of the larger overlap (dashedline in FIG. 2). For example, an I1 mark will now yield 3 peaks insteadof 1. Obviously, −I1 and −I2 spaces can no longer be detected now. A −I3space will show 1 missing peak (instead of 3). Even larger window sizes,e.g. 2.5b<w<4.5b, cause a difference of 4 peaks in space and markrun-length detection, while a −I5 space is the smallest space run-lengththat can be detected (by 1 missing peak).

Hereinafter, #+0 indicates that a run length I# yields #+0 peaks (noadditional peak), while #+1 would yield #+1 peaks for the same I# (oneadditional peak), etc. As already mentioned, this is readily detected bymonitoring violations of run-length constraints. In FIG. 4, bold linesindicate that all signals are at the saturated level (which is preferredfor optimum signal detection). Furthermore, it is to be noted that thetable in FIG. 4 corresponds to the waveforms shown in FIG. 3, wherein−90° corresponds to 270°.

It is to be noted also that the proposed phase and/or copy windowcorrection or control function may also be applied to #+1 or #+2 cases(or even higher codes) as indicated in FIG. 4. These situations maycorrespond to an asymmetric (d=0),(d=1) or a (d=0),(d=2) code withdifferent minimum run-lengths for mark and space regions, respectively,wherein the first value of d indicates the number of additional channelbit lengths by which the minimum mark run-length is increased andwherein the second value of d indicates the number of additional channelbit lengths by which the minimum space run-length is increased. Thelarger windows and larger window ranges for these codes yieldsignificantly improved power margins.

It is also to be noted that in all cases the center of the optimumwindow range (b=s) in the table of FIG. 4 corresponds to a maximumrobustness against phase errors (no effect for +/−90° error). Thus, thephase or copy window control function should preferably be adapted tomaintain the system at such a central position.

FIG. 5 is similar to FIG. 4, but gives the results for a 100% writestrategy (mark length is equal to channel bit length instead of 50% ofbit length as in FIG. 4). In the table of FIG. 5, the optimum windowrange (b=s) in the upper left corner is considerably smaller than thecorresponding region in FIG. 4 (in the middle of the left part of thetable), especially for #+0 cases. Thus, a comparison of FIG. 4 and FIG.5 demonstrates the large positive effect of a proper write strategy onthe copy window margin and hence on the power margin of a laser.

A combination of simultaneous window and phase control is even better,as in that case the averaged control data from both window and phase canbe used to keep the read-out conditions as close to their optimum (i.e.,the center of the optimum region) as possible. Now, detection of a smallphase error may directly allow a better control of the copy window andvice versa.

The different waveforms and/or pulse characteristics summarized in FIG.4 and FIG. 5 for the two different write strategies can be stored in alook-up table, either in software or in hardware, for evaluation duringread-out. However, the waveforms strongly depend on the write and readstrategies that are used for recording. Therefore, a small program couldpreferably be implemented in, for example, the disk player (for examplein one of the units 21, 22 and 25) to generate the various waveformsgiven the write and read strategies used. In an embodiment these writestrategies may be stored in prescribed regions of the disc 10, forexample in the embossed regions. The program can be called by thecomparing unit 22 as a subroutine for each waveform comparison. However,it may alternatively be used to fill or update the look-up table 23,which may be faster for evaluation during read-out. Alternatively, thewaveforms or pulse characteristics may be stored directly on the disk10.

For many combinations of write and read strategies quite simple rulescan be defined. For example, in the situation of the table shown in FIG.4 the following rules may be applied, wherein “+” and “++” indicate anincrease and a strong increase in phase or copy window sizerespectively, while “−” and “−−” indicate a decrease and a strongdecrease in phase or copy window size respectively:

first deviation in number peak of peaks phase correction windowcorrection b = s −1 −− ++ b < s +0 + + b << s +0 ++ ++ b < s +1 −− −− b<< s +1 − − b = s +1 ++ −−These rules apply for symmetric or asymmetric codes with longer minimumspace run-lengths, such as #+1, #+2, etc., and partially also for codes#+0 with the additional rule that no signal indicates that the windowmust be increased.

During MAMMOS read-out, synchronization between the bits written on thedisk 10 and the external field (and the laser power in case of a pulsedstrategy) is required. For this purpose timing fields provided on thedisk 10 and/or a wobble in the track of the disk 10 can be used. Whenphase errors in the synchronization are included in the analysis of theread-out signal by the analyzing unit 21, even small changes in the copywindow, compared to the channel bit length, can be detected andcorrected.

The analysis of the waveform of the read-out or reading signal can beapplied to written user data and/or to dedicated test areas withpredefined write strategies and/or codings provided at predeterminedpositions of the disk 10.

The described fine-tuning method for phase and/or copy window controlprovides the advantage that a correction is already possible before(partially) uncorrectable errors occur. Additionally, less averaging isrequired so that even very small non-uniformities or brief fluctuationsin field or laser power can be dealt with. In combination with ananalysis of run-length violations even large jumps will no longer be aproblem.

The present invention can be applied to any reading system for domainexpansion magneto-optical disk storage systems. Any waveformcharacteristic of the read-out signal, which indicates a change in thephase or copy window size, can be used in the analysis. The functions ofthe analyzing unit 21, the comparing unit 22, the look-up table 23 andthe control unit 25 may be provided in a single unit which may be ahardware unit or a processor unit controlled by a corresponding controlprogram. The read-out signal may be applied directly from the opticalpickup-unit 30 to the analyzing unit 21. The preferred embodiments maythus vary within the scope of the attached claims.

1. A method of controlling synchronization between an external magneticfield and data written on a magneto-optical recording medium (10), saidrecording medium comprising a storage layer and a read-out layer,wherein an expanded domain leading to a pulse in a reading signal isgenerated in said read-out layer by copying a mark region from saidstorage layer to said read-out layer upon heating by a radiation powerand with the aid of said external magnetic field, said method comprisingan analyzing step for analyzing the waveform of said reading signal, anda correction step for correcting, on the basis of the result of saidanalyzing step, a phase deviation between said external magnetic fieldand said written data.
 2. A method according to claim 1, wherein saidcorrection step is performed by shifting the timing of said externalmagnetic field.
 3. A method according to claim 1 or 2, wherein saidcorrection step is based on at least one predetermined correction rulewhich depends on a write strategy used and/or a read strategy used.
 4. Amethod according to claim 4, also comprising the step of using said atlest one correction rule for an additional copy window correction.
 5. Amethod according to claim 3 or 4, wherein said at least one correctionrule defines a correction amount and direction.
 6. A method ofcontrolling read-out from a magneto-optical recording medium (10), saidrecording medium comprising a storage layer and a read-out layer,wherein an expanded domain leading to a pulse in a reading signal isgenerated in said read-out layer by copying a mark region from saidstorage layer to said read-out layer upon heating by a radiation powerand with the aid of an external magnetic field, said method comprisingan analysis step for analyzing the waveform of said reading signal, anda controlling step for controlling a copy window size of said markcopying on the basis of the result of said analyzing step.
 7. A methodaccording to claim 6, wherein said controlling step is performed bycontrolling said radiation power and/or the strength of said externalmagnetic field.
 8. A method according to claim 6 or 7, whereinsynchronization phase errors between the external magnetic field, usedfor said mark copying, and written data are determined and used in saidanalyzing step.
 9. A method according to any one of the claims 6 to 8,wherein said analyzing step is applied to a reading signal obtained byreading a test area provided on said recording medium (10).
 10. A methodaccording to any one of the claims 6 to 8, wherein said analyzing stepis applied to a reading signal obtained by reading written user data.11. A method according to any one of the preceding claims, wherein saidanalyzing step comprises comparison of the timing of the rising edge ofa predetermined pulse of said reading signal with a reference value. 12.A method according to any one of the preceding claims, wherein saidanalyzing step comprises comparison of the duration of a predeterminedpulse of said reading signal with a reference value.
 13. A methodaccording to claim 11 or 12, wherein said predetermined pulse is thefirst pulse of a code run-length.
 14. A method according to claim 12,wherein said duration is determined by detecting the pulse amplitude ofsaid predetermined pulse after a filter operation.
 15. A methodaccording to any one of the preceding claims, wherein said analyzingstep is performed by using information from a look-up table (23).
 16. Amethod according to claim 15, wherein said look-up table (23) is updatedon the basis of information read from said recording medium (10).
 17. Amethod according to claim 15, wherein said information defines arelation between said waveform and at least one of a phase error and acopy window size.
 18. A method according to any one of the claims 15 to17, wherein said look-up table is provided by a control program of adriver function used for generating said external magnetic field.
 19. Amethod according to any one of the preceding claims, also comprising thestep of storing on said recording medium (10) strategy informationdefining a write strategy of said recording medium (10), and using saidstrategy information in said analyzing step.
 20. A method according toclaim 19, wherein said strategy information is used for generating areference waveform used in said analyzing step.
 21. A reading apparatusfor controlling synchronization between an external magnetic field anddata written on a magneto-optical recording medium (10), said recordingmedium comprising a storage layer and a read-out layer, wherein anexpanded domain leading to a pulse in a reading signal is generated insaid read-out layer by copying a mark region from said storage layer tosaid read-out layer upon heating by said radiation power and with theaid of said external magnetic field, said apparatus comprising:analyzing means (21-23) for analyzing the waveform of said readingsignal, and correction means (25) for correcting a phase deviationbetween said external magnetic field and said written data on the basisof the result of said analyzing step.
 22. A reading apparatus forcontrolling read-out from a magneto-optical recording medium (10), saidrecording medium comprising a storage layer and a read-out layer,wherein an expanded domain leading to a pulse in a reading signal isgenerated in said read-out layer by copying a mark region from saidstorage layer to said read-out layer upon heating by a radiation powerand with the aid of an external magnetic field, said apparatuscomprising: analyzing means (21-23) for analyzing the waveform of saidreading signal; and control means (25) for controlling a copy windowsize of said mark copying on the basis of the result of said analyzingstep.
 23. A reading apparatus according to claim 21 or 22, wherein saidanalyzing means (21-23) comprises storing means (23) for storinginformation defining a relation between said waveform and at least oneof a phase error and a copy window size.
 24. A reading apparatusaccording to claim 23, wherein said analyzing means (21-23) comprisescomparing means (22) for comparing said analyzed waveform on the basisof said relation stored in said storing means (23).
 25. An apparatusaccording to any one of the claims 21 to 24, wherein said readingapparatus is a disk player for MAMMOS disks.
 26. A magneto-opticalrecord carrier comprising a storage layer and a read-out layer, whereinan expanded domain leading to a pulse in a reading signal is generatedin said read-out layer by copying a mark region from said storage layerto said read-out layer upon radiation heating and with the aid of anexternal magnetic field, said record carrier (10) comprisingpre-recorded control information defining a relation between a waveformof said reading signal and at least one of a phase error and a copywindow size.
 27. A record carrier according to claim 26, wherein saidcontrol information comprises a strategy information defining a writestrategy of said record carrier (10).
 28. A record carrier according toclaim 26 or 27, wherein said record carrier is a MAMMOS disk (10).